In disc drives, a read/write head flies over a disc surface at a fly height. As the areal density of disc drives increases with newer designs, there is an increasing need to provide lower fly heights in order to read data with the increased areal density. With the lower fly heights, there is an increased danger of the read/write head crashing into the disc if there are deviations from flatness of the disc surface.
In disc drives that include a stack of multiple discs, it is found that there are particular problems with flatness of the discs at the ends of the stack (outer discs) that are in direct contact with clamps. The clamping forces distort the outer discs. In the past, these problems with the outer discs were less severe because fly heights were greater. With the increasing areal density in new designs, however, fly heights are smaller and the outer disks must meet more stringent flatness requirements.
A method and apparatus are needed to reduce warping of outer discs in a disc stack, and to provide improved flatness of the outer discs surfaces. Embodiments of the present invention provide solutions to these and other problems, and offer other advantages over the prior art.